The invention relates to a hybrid bearing in the form of a combination of a slide bearing and a magnetic bearing, for example, for use in bearing the revolving units of an underwater power generation plant, and a method for its production.
Underwater power generation plants are used for power generation, especially electric power generation, from a sea or ocean current, with tidal currents being considered for the latter. In the present application, an underwater power generation plant shall be understood as being a turbine/generator unit which is attached to a support structure, with water flowing freely around the same, and for which no dam structure is required. The foundations for the support structure can either be laid on the ground of the water body or a floating unit is used alternatively which can be held in position by means of anchoring. The revolving water turbine of such a power generation plant must be held in such a way that the absorbed current forces and the weight of the water turbine, including the shaft components connected with the same, are supported in a secure manner.
In the case of a directly driven underwater power generation plant, no transmission is interposed between the electric generator and the water turbine, so that the rotor unit of the electric generator forms a modular unit with the water turbine and especially a hub-like support structure. Consequently, the forces caused in this configuration by the electric generator need to be intercepted by the bearings for the module consisting of water turbine and generator rotor.
There is a necessity for underwater power generation plants that they are provided with a sturdy configuration in order to limit to an absolute minimum or avoid entirely the mostly difficult maintenance work. This leads to a demand on the bearing of such an installation that it is arranged to be failure-proof in the prevailing ambient conditions in a flow that mostly transports sediments and sand. In the case of an underwater power generation plant which is arranged in an ocean current, the problems concerning a corrosive salt water environment is added to this difficulty. The mentioned requirements for the bearings also occur in other heavy-duty machines which are provided especially for the use under rough ambient conditions.
Bearings for the use in underwater power generation plants are often arranged as single-row or multiple-row rolling bearings. However, the rolling bodies used in rolling bearings are often susceptible to the abrasive effect which is caused by the sediments penetrating the bearing. A high amount of effort needs to be employed in sealing such bearings. In order to provide bearings with a robust configuration it was proposed in US 2007 0007772 A1 for example to use a slide bearing in which water is pressed between the bearing surfaces in order to form a water film. With the help of this bearing, an external rotor which consists of two rotors and comprises an arrangement of permanent magnets is held in the respective support ring on a gondola body in which the stator components are housed. The disadvantageous aspect in such a hydrodynamic slide bearing is however that even in the case of pumps of large configurations a sufficiently stable lubricant film between the bearing surfaces cannot be maintained permanently in many cases at low revolving speeds of the water turbine and consequently a mixed frictional state is obtained in the bearing with percentages of dry friction and wet friction, leading to respective bearing losses. It is a further disadvantage that the pump units associated with the bearing need to be provided very powerful configuration and further represent additional components with respective failure probability for the underwater power generation plant.